Conventionally, various molded articles have been known as a molded article containing a plant material and a thermoplastic resin. By mixing the plant material along with the thermoplastic resin, excellent bending resistance, impact resistance and deformation resistance can be given to the molded article.
In order to produce the molded article which is more excellent in the above-described various performances, it is considered better to mix a large amount of the plant material. Generally, an extrusion forming method and a press forming method have been used as the method for producing the molded article containing a large amount of the plant material. Where the content of the plant material is increased, the fluidity of a molding material lowers, but with these methods, the molding material exhibiting a low fluidity can be formed. The molded articles obtained with the extrusion forming method and the press forming method, are low in degree of freedom of configuration. With an injection molding method, molded articles, each exhibiting a high degree of freedom of configuration, can be obtained, but it is very difficult to inject a molding material containing a large amount of plant material, and exhibiting a low fluidity.
Molded articles, each containing a plant material and a thermoplastic resin and being formed with injection molding, have been also proposed (see Patent Document 1, for example). Patent Document 1 discloses that by relatively decreasing the content of the plant material, the injection molding becomes possible. Patent Document 1 discloses that the molding material containing a plant material in an amount of 10 to 30% by mass when the total amount of the molding material is taken as 100% by mass can be subjected to injection molding, and that the molding material which contains a plant material in an amount of 60% by mass when the total amount of the molding material is taken as 100% by mass cannot be subjected to injection molding. Thus, conventionally, molded articles, each containing a large amount of the plant material and exhibiting high degree of freedom of configuration, have not been able to be obtained.
And, in recent years, in consideration of environmental problems, such as increasing of emission amount of carbon dioxide, etc., it has been proposed to give more excellent biodegradability to molded articles, using polylactic acid resin as the thermoplastic resin. However, polylactic acid resin is expensive. Therefore, if the mixing ratio of polylactic acid resin is increased, the production costs of the molded articles increase. In addition, polylactic acid resin is inferior in heat resistance so that in order to give heat resistance to the molded articles containing polylactic acid resin, a crystallizing step such as an annealing treatment, etc. is needed. Therefore, where polylactic acid resin is used as the thermoplastic resin, there is exhibited the problem that the production costs of the molded articles become very expensive.
Patent Document 1: Patent application laid-open No. 2005-105245